The Apache HTTP Server, commonly referred to as Apache, is a popular open source web server software. mod_isapi is a core module of the Apache package that implements the Internet Server extension API. The extension allows Apache to serve Internet Server extensions (ISAPI .dll modules) for Microsoft Windows based hosts.

By sending a specially crafted request followed by a reset packet it is possible to trigger a vulnerability in Apache mod_isapi that will unload the target ISAPI module from memory. However function pointers still remain in memory and are called when published ISAPI functions are referenced. This results in a dangling pointer vulnerability.

Successful exploitation results in the execution of arbitrary code with SYSTEM privileges.

Proof of Concept.

Proof of concept code is available for this vulnerability. The payload will write a text file (sos.txt) to the Apache working directory demonstrating that code execution is possible. The code can be downloaded from the following link: